79;4 THE POPULAR SCIENCE MONTHLY. 



compact mass of the vegetative body, devoid of leaves or leaf- 

 like appendages, exposes the least possible evaporating surface to 

 the sun ; the thick skin, bearing only a few scattered stomata, 

 breathing pores, wraps an almost impermeable covering round 

 the internal moisture ; the long, wiry, fibrous roots run hither 

 and thither through the sand and into the finest crevices of rocks ; 

 and further, the bristling, spiny armor shields the plant from men 

 and beasts. All this and much more goes to make up the plant 

 of plants that is best fitted to fulfill the mission of vegetation in 

 the Southwestern borderlands. And so the problem solves itself, 

 and we come to realize why the progenitors of the Cactacece, 

 spread out and multiplied far and wide, and broke into a myriad 

 varied forms, all retaining amid their diversity the distinctive 

 characteristics of the primal type. 



A standard British encyclopaedia of scarcely three quarters of 

 a century ago vouchsafes the statement that the order Cactacece 

 embraces "twenty-seven" species. Grasp the contrast between 

 this day of science and that ! The botanists of the Century Dic- 

 tionary estimate the species at far above the thousand mark. 

 For this vast stride we thank a host of indefatigable explorers, 

 and of these, a large share of credit goes to the scientists of the 

 Mexican Boundary and the Pacific Railway Surveys, whose dis- 

 coveries were the main foundations of the labors of Engelmann. 

 Thus duly recognizing the scope of the field before us, we may 

 with interest follow an outline sketch of the order. The general 

 character of the vegetative body may be passed over for the 

 present without further detail, that we may the more particu- 

 larly notice the floral structure on which the systematic study of 

 the order so largely depends. The inferior ovary, surmounted by 

 the sepals, petals, and stamens, places the order immediately 

 among the highest of the dicotyledonous CJioripetalce*. There is 

 a natural division into two suborders. In the first, the Rotatce,, 

 the rotate many-leaved calyx and corolla, with the stamens, 

 directly surmount the ovary. In the second there is a unique 

 and obviously progressive development: calyx and corolla are 

 united toward their bases and prolonged into a tube, with the 

 stamens inserted on its throat whence the name of the sub- 

 order, the Tubuloscz. The typical Eotatcz are the widespread ge- 

 nus Opuntia, numbering about two hundred and fifty species. 

 The greater part of the genus are characterized by broad, thick- 

 ened, fleshy, jointed stems ; but a small subgenus, and this prob- 

 ably the less highly specialized, have cylindrical joints. Most of 

 the species are more or less spreading and prostrate, but a large 

 number are truly arborescent in growth. Several species are 

 thoroughly naturalized in the northeastern quarter of the United 

 States, and these are among the most brilliant acquisitions of our 



